docs: def Confinement(D, rhol, rhog, sigma, g=g):
      r'''Calculates Confinement number or `Co` for a fluid in a channel of 
      diameter `D` with liquid and gas densities `rhol` and `rhog` and surface
      tension `sigma`, under the influence of gravitational force `g`.
  
      .. math::
          \text{Co}=\frac{\left[\frac{\sigma}{g(\rho_l-\rho_g)}\right]^{0.5}}{D}
  
      Parameters
      ----------
      D : float
          Diameter of channel, [m]
      rhol : float
          Density of liquid phase, [kg/m^3]
      rhog : float
          Density of gas phase, [kg/m^3]
      sigma : float
          Surface tension between liquid-gas phase, [N/m]
      g : float, optional
          Acceleration due to gravity, [m/s^2]
  
      Returns
      -------
      Co : float
          Confinement number [-]
  
      Notes
      -----
      Used in two-phase pressure drop and heat transfer correlations. First used
      in [1]_ according to [3]_.
  
      .. math::
          \text{Co} = \frac{\frac{\text{surface tension force}}
          {\text{buoyancy force}}}{\text{Channel area}}
  
      Examples
      --------
      >>> Confinement(0.001, 1077, 76.5, 4.27E-3)
      0.6596978265315191
  
      References
      ----------
      .. [1] Cornwell, Keith, and Peter A. Kew. "Boiling in Small Parallel 
         Channels." In Energy Efficiency in Process Technology, edited by Dr P. 
         A. Pilavachi, 624-638. Springer Netherlands, 1993. 
         doi:10.1007/978-94-011-1454-7_56.
      .. [2] Kandlikar, Satish G. Heat Transfer and Fluid Flow in Minichannels 
         and Microchannels. Elsevier, 2006.
      .. [3] Tran, T. N, M. -C Chyu, M. W Wambsganss, and D. M France. Two-Phase 
         Pressure Drop of Refrigerants during Flow Boiling in Small Channels: An 
         Experimental Investigation and Correlation Development." International 
         Journal of Multiphase Flow 26, no. 11 (November 1, 2000): 1739-54. 
         doi:10.1016/S0301-9322(99)00119-6.
      '''
      return (sigma/(g*(rhol-rhog)))**0.5/D